Conventionally, a bearing is used to rotatably hold a rotor shaft of a rotor, and a stator housing is used to fix the bearing in a stator. The bearing is provided in a cylindrical member of the stator housing so as to rotatably hold the rotor shaft, and a stator core is attached on an outer circumferential face of the cylindrical member.
The stator housing is made of suitable metal, e.g., brass, which can be easily processed and formed into various shapes. A sintered bearing is press-fitted into the stator housing, and the stator core is fitted on an outer circumferential face thereof and fixed by an adhesive.
On the other hand, some stator housings are not made of metal, e.g., brass, and they are made of resin so as to reduce production cost. To prevent the bearing from being moved in an axial direction with respect to the stator housing, a bearing structure, in which a retainer for prohibiting the bearing to move in the axial direction is provided to one end of the stator housing, has been invented (see Patent Document 1).